1. Field of the Invention
This invention relates to apparatus for recovering metal from a bath or liquid solution, and more particularly to portable apparatus which may conveniently be immersed into and removed from a metal bearing solution but which is so arranged as to inhibit tampering and unauthorized removal of recovered metal. Since the invention is intended primarily for recovery of silver, the following disclosure will refer to a silver recovery apparatus, although those skilled in the art will readily appreciate that the apparatus may be adapted as well for the recovery of other metals.
2. Description of the Prior Art
It is well known that photographic fixing solutions wash silver from unsensitized areas of exposed film. The silver bearing fixer, when it is spent, is either disposed of or is processed by any of a variety of recovery systems by which the silver is removed from the solution so that both the silver and the solution may be reused.
Referring to one known system described in U.S. Pat. No. 3,926, 768, silver is recovered from spent photographic solutions by feeding the spent solutions into a pre-collecting vessel where the solution collects until a predetermined volume has been received, at which time it is automatically dispensed, by a self-triggering syphon, into an electrolysis chamber, and direct current is automatically turned on for a predetermined period of time between an anode and a cathode in the chamber to plate out the silver onto the cathode while a magnetic agitator is energized to maintain the unplated silver in suspension in the solution. The system thus disclosed is intended for permanent installation and is complicated by a pre-collection chamber and equipment for effecting self-triggering syphoning automatically to dispense a predetermined volume of solution from the pre-collection chamber to an electrolysis chamber. This patent also describes other known systems for removing silver from solutions, and notes the disadvantages associated with each.
In the development of this technology those skilled in the art recognized the need for a small, economical, and portable recovery unit. Thus, such a unit has been developed wherein a cathode and an anode depend from an upper housing which can be removably mounted on a container for the solution. The cathode is rectangular in horizontal cross-sections and is open at its lower end, while the anode is a cylindrical rod disposed within the cathode. A propeller is also mounted within the confines of the cathode and is intended to circulate solution from the container in the area confined within the cathode during electrolysis.
An important disadvantage of this type of portable unit resides in the fact that since the anode is not equidistantly spaced from the inner surfaces of the cathode, but rather is closer to certain areas of the cathode than to other such areas, the silver, as it is plated out of solution, builds up on those areas of the cathode immediately adjacent the anode and eventually shorts out the electrolysis circuit terminating the process while a substantial area of the cathode is hardly plated with silver, if at all.
Another problem that, as far as I am aware, has not been dealt with by innovators in the art is the possibility of tampering with recovery apparatus and removing therefrom the high purity, and therefor quite valuable, plated silver. Thus, when electrolysis is completed, the cathode is normally withdrawn from the unit and sent to a facility at which the silver is removed. However, in many recovery units, and especially portable units of the type referred to above, it is a simple matter to lift the unit from the solution and, since the bottom of the cathode is open, to scrape the plated silver off its inner surface, particularly since the majority of the silver tends to plate onto a relatively small surface area of the cathode.